Little is known of his life. Around 1544 he worked at the Bruges cathedral. Thereafter and until 1549 he was choirmaster at the court of Charles V, where he preceded Nicolas Gombert. Later he was employed by the Marian Brotherhood in 's Hertogenbosch.
His nickname non Papa was jokingly added to distinguish him from the contemporaneous Pope Clement VII.
Clemens was one of the chief forerunners of Palestrina and Orlandus Lassus. He was a prolific composer, writing: